New And Significant Accounting Policies (Components Of Net Periodic Benefit Cost) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 98		$ 82		$ 197		$ 164
Interest cost	165		164		329		328
Expected return on plan assets	(150)		(167)		(299)		(334)
Amortization of prior service cost	5		9		10		18
Amortization of unrecognized loss	32		12		63		24
Net periodic benefit cost	150		100		300		200
Less: transfer to regulatory account	(75)	[1]	(36)	[1]	(150)	[1]	(72)	[1]
Total	75		64		150		128
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	11		11		23		22
Interest cost	21		23		42		46
Expected return on plan assets	(20)		(20)		(39)		(40)
Amortization of transition obligation	6		6		12		12
Amortization of prior service cost	6		6		12		12
Amortization of unrecognized loss	2		1		3		2
Net periodic benefit cost	26		27		53		54
Total	$ 26		$ 27		$ 53		$ 54

[1] The Utility recorded these amounts to a regulatory account since they are probable of recovery from customers in future rates.